2015年尼泊尔MW7.8地震前磁扰动极化异常特征分析  

PRE-SEISMIC POLARIZATION CHARACTERISTICS OF MAGNETIC DISTURBANCE OF THE 2015 MW7.8 NEPAL EARTHQUAKE

作　　者：管贻亮 董晓娜[1] 尹玉振 冯丽丽[2] 殷海涛[1] GUAN Yi-liang;DONG Xiao-na;YIN Yu-zhen;FENG Li-li;YIN Hai-tao(Shandong Earthquake Agency,Jinan 250014,China;Qinghai Earthquake Agency,Xining 810001,China)

机构地区：[1]山东省地震局,济南250014 [2]青海省地震局,西宁810001

出　　处：《地震地质》2021年第5期1311-1325,共15页Seismology and Geology

基　　金：基金资助:2019年度中国地震局监测、预报、科研三结合课题(3JH-201901084);中国地震局地震科技星火计划项目(XH20062);山东省地震局科研基金(JJ1803Y)共同资助。

摘　　要：文中基于中国大陆地区48个台站的地磁秒值资料,采用极化法对2015年尼泊尔MW7.8地震前的磁扰动特征进行了分析。极化法的逐步计算结果与地磁K指数的对比分析表明极化高值异常与空间磁场活动之间没有相关性,可用于提取震磁异常信息。距震中1500km范围内台站的极化值在震前98d出现了同步性高值异常,考虑到磁场变化具有区域同步性,提出了极化逐日相关分析。研究发现地震孕育过程中各台站间的极化相关性明显增强,而地震发生在同步性转折阶段。基于极化值相对变化量进行的空间异常分析显示,尼泊尔地震前>20%的台站出现持续3d以上的异常,且具有明显的区域性特征。文中从构造动力演化角度对地磁极化异常的孕育和发展进行了解释,对磁场变化机理进行更进一步的探索。研究认为,多台同步性极化异常和逐日相关转折对强震具有重要的指示意义,该成果能为强震监测预测提供新的技术途径。On April 25,2015,a strong earthquake with magnitude 7.8(MW)and focal depth of 8.2km(according to USGS)occurred in Nepal(28.15°N,84.71°E),which caused heavy casualties and property losses to Nepal,China,and some neighboring countries.The focal mechanism solution shows that the earthquake is a low-angle thrust earthquake,resulting from the collision and following long-term compression between the Indian Plate and Eurasian Plate.In this paper,we analyze the magnetic disturbance characteristics before the Nepal MW7.8 earthquake using polarization method based on the geomagnetic second data of 48 stations in China's Mainland.Polarization method uses the ratio of the vertical component(Z)to the horizontal component(H)of the geomagnetic field,i.e.Z/H.This method can suppress external interference and thus extract seismo-magnetic anomaly information.Previous geophysical studies have shown that the perturbation in geomagnetic field during the earthquake preparation has a far greater impact on Z than H.The high polarization anomaly may contain some magnetic field information related to earthquake preparation.The calculation of geomagnetic second data includes three main parts:spectrum analysis,polarization calculation and abnormal signal extraction.The dominant frequency band(0.01~0.2Hz)is selected for subsequent calculation and analysis.(1)By analyzing the relationship between the polarization and the perturbation in the geomagnetic field through spectrum analysis,we find that the polarization value at each stage is obviously negatively correlated with the geomagnetic K index,indicating that the high polarization anomaly is almost not related to the geomagnetic activity and therefore can be used to analyze the pre-seismic anomaly.In order to ensure the reliability of the calculation results,it is recommended that the data length should exceed 1 year,based on the annual variation characteristics of polarization value.(2)The polarization value of the Lhasa station(epicentral distance of 628km)and the Shiquanhe station(epi

关 键 词：地震地磁 极化法 尼泊尔MW7.8地震 逐日相关 

分 类 号：P315.721[天文地球—地震学]